Field
The present invention relates to an information communication system, an information communication program, and an information communication method, and in particular, to an information communication system and the like capable of securely providing an encryption password for an attachment file attached to a transmission information such as an e-mail or the like, toward a transmission destination.
Description of the Related Art
Conventionally, as a method of transmitting and receiving an electronic file, there is a method of attaching an electronic file to an e-mail to transmit an e-mail with an attachment file attached thereto. In the case of transmitting and receiving an electronic file including confidential information, the electronic file may be attached to an e-mail after being encrypted. As a method of encrypting an electronic file, there is a common key encryption method. The common key encryption method is a method wherein a same (common) password at the time of encryption and at the time of decryption of an electronic file is used.
In the case of transmitting and receiving an electronic file encrypted by using the common key encryption method, a password is determined on the transmitting side, and the password is transmitted to the receiving side. The method of describing a password in the main text (text sentence) of an e-mail and communicating the password to the reception side is not always secure. This is because a possibility that a third party take a peek the message body cannot be excluded due to the nature of the e-mail which communicates information through the Internet.
As a method for securely informing a key information such as a password to the reception side, for example, there has been proposed a method of encrypting an e-mail or an attachment file, then dividing the decryption key into two parts, transmitting one part of the key together with the encrypted e-mail, and transmitting the other part of the key together with another e-mail (for example, refer to Patent Document 1: JP 2001-60944 A). According to this, it is taught that the risk that the decryption key is intercepted can be reduced compared with a case of transmitting the decryption key in one e-mail.
In the method disclosed in Patent Document 1, however, since the decryption key itself is not encrypted but transmitted in plaintext, there still remains the risk that the decryption key is leaked. In particular, in a case where both of the two e-mails transmitted which the decryption key divided into two parts are intercepted, leakage of the decryption key cannot be avoided.
The invention has been made in view of the above circumstances, and it is an exemplary object of the invention to provide an information communication system, an information communication program, and an information communication method capable of more securely informing a password, which is used for encryption of an attachment file attached to transmission information, to a destination while preventing interception by a third party through use of a conventional information transmitting and receiving method, such as an e-mail software.